This invention relates generally to antennas and more particularly to antennas that operate over a wide frequency range. Most high frequency (HF) communication systems use very large antennas or several smaller antennas to cover the entire HF spectrum (2 to 32 megaHertz (MHZ)). Oil board military ships, where space is at premium, this configuration of antennas poses considerable problems in the form of prohibiting certain deck maneuvers, interfering with weapons systems, and detracting from stealth characteristics.
Another problem for an antenna system designed to operate over a very wide frequency range is the impedance matching of the system with that of a transmitter. In the past, compensating or matching circuits have been designed to be used with an antenna to accomplish impedance matching. Typically, such matching circuits are useful only over a narrow range of frequencies. Hence, for a wideband antenna, a number of such compensators are required as well as an appropriate switching system that permits the proper matching circuit to be used for whatever transmitting impedance is present.
Thus, for at least shipboard applications, it is desirable to have a single antenna apparatus that covers a very wide frequency range and that provides acceptable impedance matching over this frequency range without the need for a myriad of impedance matching circuits and their required switching arrangements.
The invention accomplishes these goals by utilizing a tapered, folded monopole antenna configuration. In this configuration, one of two vertical monopole antenna elements is tapered and resistively loaded to a ground plane. In a preferred embodiment of the invention the tapered vertical monopole antenna element includes a series of operably coupled cylindrical sections that extend from a base end of this element to its top end. The cylindrical sections decrease in diameter from the base end to the top end of the tapered element. The second monopole antenna element has a substantially constant outer diameter. An antenna feed is coupled to the base of this second element via a transformer. A third antenna element of substantially equivalent diameter to the second element is operably coupled to the top ends of the first and second antenna elements. In both transmitting and receiving modes the tapered monopole antenna element is considered to cause a cancellation of the electric field from the feeding antenna element to thereby provide a wide range of impedance matching. The resistive load applied to the ground isolated tapered antenna element could be replaced by multiple loadings such as those involving R, L, and C components arranged in numerous combinations and embodiments. Besides using a stepwise tapered element, the antenna of the invention could employ a continuously tapered element.
It is an object of this invention to provide an antenna system suitable for use with communications operating over a very broad band of frequencies.
Another object of this invention is to provide an antenna system suitable for use with communications operating over the entire high frequency band.
Another object of this invention is to provide a single antenna that operates over a very wide frequency band and that provides impedance matching over this wide frequency band.
Another object of this invention is to provide a single antenna in which impedance matching is performed without the need for a multitude of impedance matching circuits.
Another object of the invention is to provide a single antenna in which said impedance matching is provided without the need for band switching circuits.
Other objects, advantages and new features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanied drawings.